Torsional vibration damping mechanisms have long been used to reduce the adverse effects of torsional vibrations or fluctuating torques in vehicle drivelines. Such torsional vibrations or fluctuating torques, hereinafter referred to as torsionals, emanate primarily from engine power pulses and torque spikes, and from abrupt changes in driveline torque due primarily to rapid engine acceleration/deceleration and transmission ratio changes.
Such mechanisms commonly employ a spring(s) to attenuate torsionals and transmit positive and negative torque between the vehicle engine and wheels, and employ a damper assembly to control the rate of flexing of the springs. Examples of such mechanisms may be seen by reference to U.S. Pat. Nos. 4,874,074 and 4,690,256; and French patent application 2,611,013. These documents are incorporated herein by reference.
The mechanisms in the U.S. documents each employ a nested pair of spiral wound springs formed of steel; these springs are designed to withstand flexing of forty or more degrees, flex radially inward and outward in response to increasing positive and negative torque, and are symmetrically balanced when paired.
The mechanism in the French Patent document employs a single spiral wound spring formed of a composite material including a plurality of layers of reinforcing filaments bonded together by a plastic material; this spring has an unknown flex design limit, flex radially inward and outward in response to increasing positive and negative torque, and is not per se symmetrically balanced.
The steel spiral wound springs in the mechanism of the U.S. patent documents have the disadvantage of increasing the inertia of the damping mechanism. The composite spring in the mechanism of the French patent document has the disadvantage of being per se symmetrically unbalanced, is difficult to install in a damper mechanism for flexing in only one direction, and is prone to delamination failure of the reinforcing filaments due to flexing in both directions.
Several problems have been encountered concerning attachment of composite spring ends and, particularly, problems encountered in the attachment of composite spring ends in the limited available space of a vehicle driveline torsional damping mechanism. In some applications manufacturing costs are increased when holes have to be drilled in the spring ends to effect end attachment by fasteners such as screws or bolts. Such drilling may also weaken the spring ends and reduce the life of the spring. Also, as in the above mentioned French patent document, a substantial portion of the length of the composite spring is devoted to end attachment, thereby reducing the effective or active length of the spring and reducing the space available for the active portion of the spring.